The present invention relates generally to sidebar locks, and more particularly, to a sidebar lock including a sidebar which includes a longitudinal interruption at or near the longitudinal midpoint of the sidebar which interrupts any inclined plane formed by the sidebar being canted when a key coded different from the correct code is inserted into the lock barrel.
Traditional sidebar locks include a lock barrel, a stationary sleeve extending around the lock barrel, and a spring biased sidebar on the lock barrel which projects into a slot in the sleeve to prevent rotation of the lock barrel unless a mating key is present in the lock barrel. The lock barrel is coupled to an output mechanism which, by way of example, can be a vehicle ignition switch, a latch for a vehicle door, deck, hatch, lift gate or tail gate, the bail on a padlock, levers on panel locks, residential and commercial door latches, etc. For example, the lock barrel can have a lever or drive shaft attached thereto. The lever can be linked to the latch by a rod or cable arrangement. The drive shaft can be coupled with a latch or with a cable drive to the latch.
One such sidebar lock is illustrated in FIGS. 28 and 29, which are labeled xe2x80x9cPrior Artxe2x80x9d. The sidebar lock is mechanically unlocked by a mating or xe2x80x9ccorrectxe2x80x9d key (not shown) inserted into the lock barrel 122 for aligning a plurality of tumblers 124 to withdraw a sidebar 126 from a sidebar groove 129 in a sleeve 130. The sidebar 126 prevents rotation of the lock barrel in the absence of the xe2x80x9ccorrectxe2x80x9d key in the lock barrel. The sidebar lock illustrated in FIGS. 28 and 29 has a key 120 with nearly the same code as the xe2x80x9ccorrectxe2x80x9d key, commonly called a cousin key, inserted into the lock barrel. As will be described, for such condition, the sidebar 126 can be retracted partially from the sidebar groove 129 in the sleeve at an inclined angle to the axis of the lock barrel as shown in FIG. 28.
The tumblers 124 include notches 127 which are normally out of alignment with an edge 128 of the sidebar so that the tumblers 124 force the sidebar radially outward, against the force of sidebar bias springs 131 and 132 into the sidebar groove 129 in sleeve 130. In such position, the sides 133 and 134 of the sidebar 126 cooperate with the sides of the sleeve groove to prevent the lock barrel from rotating relative to the sleeve. The xe2x80x9ccorrectxe2x80x9d key aligns tumblers 124 in the lock barrel 122, allowing the edge 128 of the sidebar 126 to be received in the notches 127, permitting the sidebar to be retracted into the lock barrel. With the sidebar retracted, the lock barrel can be rotated within the sleeve 130 to actuate the output mechanism.
Depending upon the number and location of the tumblers 124 supporting the sidebar 126, the sidebar can be retracted partially from the sidebar groove 129 in the sleeve at an inclined angle to the axis of the lock barrel as shown in FIG. 28. This is particularly true when a key, such as a cousin key 120, with nearly the same code as the xe2x80x9ccorrectxe2x80x9d key, is used. For such condition, the surface of edge 138 of the sidebar forms an inclined plane which bridges the shear line 140 between the lock barrel and the sleeve. The inclined plane formed by edge 138 allows relative sliding movement between the sidebar and the sleeve, causing the sidebar to be driven into the lock barrel if the lock barrel is forcibly rotated. To reduce this occurrence, lock manufacturers generally limit the number of usable key codes so that very similar keys are not produced.
The prior art sidebar lock, shown in FIG. 28, includes a conventional sidebar, such as the sidebar 126 shown in FIGS. 30-33. The sidebar is biased into the barrel lock by bias springs 131 and 132 which are supported on mounting surfaces 141 and 142 of the sidebar defined by reduced height portions located at opposite ends of the sidebar. The springs 131 and 132 can be held in place by spring clips 136. The edge 138 of the sidebar 126 can be forced out of the sidebar groove when the lock barrel is forcibly rotated when a cousin key is present in the keyslot, with the inclined edge 138 of the sidebar sliding along the surface of the sleeve 130, whereby the sidebar is forced into the lock barrel.
Because of the reduced height end portions of the prior art sidebar 126, the engagement of the sidebar 126 with the groove 129 in the sleeve 130 is limited by this design. This significantly decreases the effort required to forcibly rotate the lock barrel when a cousin key is present in the key slot, with the inclined edge 138 of the sidebar sliding along the surface of the sleeve 130, thereby forcibly driving the sidebar into the lock barrel.
Forcibly driving the sidebar into the lock barrel can cause the sidebar to be plastically deformed at edge 128 of the sidebar 126 at the point of engagement with the tumblers and/or compress the tumbler springs 143, thus defeating the locking function.
When a key having a code that is very similar to the correct code is used, the rotational force required to defeat the locking function is a small fraction of the rotational force the lock can normally withstand. Accordingly, manufacturers are limited in the number of key codes they can offer. The present invention significantly increases the number of robust key codes. The greater the number of robust codes available, the greater the security of the lock.
The disadvantages and limitations of the background art discussed above are overcome by the present invention. With this invention, there is provided a new and improved sidebar lock which comprises a sleeve including a sidebar groove extending longitudinally along a surface of the sleeve and a lock barrel supported within the sleeve for rotation relative to the sleeve. The lock barrel is adapted for connection to an output mechanism. The sidebar lock includes a sidebar which is movable radially relative to the lock barrel between an extended position in which an edge of the sidebar extends into the sidebar groove and cooperates with the sidebar groove to prevent relative rotation between the lock barrel and the sleeve, and a retracted position in which the sidebar is retracted into the lock barrel, permitting relative rotation between the lock barrel and the sleeve. In accordance with the invention, either the edge of the sidebar or a surface of the sleeve adjacent to the sidebar include an interruption. In one embodiment, the interruption is a gap in an edge surface of the sidebar. In another embodiment, the interruption is an indentation in an edge surface of the sidebar. In a further embodiment, the interruption is provided by widening the sidebar groove in the sleeve.
The surface interruption negates the effect of an inclined plane, formed as the result of the sidebar being partially withdrawn from a sidebar groove in the sleeve such that the sidebar extends at an angle relative to the axis of the lock barrel. Without such surface interruption, a key having a coding similar to the coding for the mated key for the lock, can cause the sidebar to be slid along the surface of the sleeve and be driven out of the sidebar groove.
The present invention significantly increases the number of robust key codes. The greater the number of robust key codes that are available, the greater the security of the sidebar lock.